deploy-sourcegraph-dhall: postgres: implement generate reading from config
Created by: uwedeportivo
right now the generate function in prometheus https://github.com/sourcegraph/deploy-sourcegraph-dhall/blob/master/src/base/postgres/generate.dhall doesn't read the configuration that is passed into it.
we want to read enough configuration to support configuring these params:
- implement templating logic
- maybe add more fields in the global config
- if needed: implement transformations
provide an example pipeline config that declares the changes from dogfood for postgres.